1. Field of the Invention
This invention relates to telephone subscriber loop testing systems and, in particular, to a device for determining whether a fault in the subscriber loop is located between a telephone central office and the device or between the device and terminal equipment.
2. Description of the Prior Art
It is useful to know whether a fault in a telephone subscriber loop is located within the customer's premises or outside the premises so that an appropriate repairperson may be assigned to correct the fault. Known methods use a device, known generally as a maintenance termination unit (MTU), for the disconnection of the loop at the customer's premises and the connection of an impedance termination network across the conductors of the loop by means of relay contacts. In some MTU's, the termination network is connected permanently across the loop conductors.
If a loop is determined to be faulty on testing, the MTU is activated in response to an activate signal transmitted from a testing source--either at the telephone central office or a test center remotely located from the central office. That section of the loop between the central office and the MTU is tested again; if no fault is detected in this section, the fault is determined to be in the loop section between the MTU and the telephone set.
A problem with this method lies in the reliability of the MTU: making connection through relay contacts does not always insure a perfect connection because of dust or wear and tear; and reliability of component parts is another problem. Another problem relates to the increased time taken for testing because of mechanical operation. A further problem relates to the necessity for maintaining administrative records to determine whether a loop is equipped with such a device.